In known suction devices of this type, operating on the side-channel compressor principle, the intake orifice and the outlet orifice of the casing are on the edge of the casing, specifically at the ends of the side channel arrangement which runs in the direction of the circumference and is aligned radially with the location of the side-channel compressor vanes. For many applications, and especially for use in dentistry, it would be desirable to have available a suction device of this kind in which the intake orifice is on the central axis of the casing. Such a suction device combined with another unit, such as a separator for liquids, could form a very compactly built unit in its radial dimension. If one were simply to provide such a channel in the casing, leading in a radial direction from a central intake orifice to the intake end of the side channel arrangement, then this would have to be enlarged in its axial dimensions and there would be losses in efficiency due to the sharp diversion of the airstream.